Brown Rot Blossom and Twig Blight

Pathogens: Monilinia laxa and Monilinia fructicola

Blossom and twig blight cause the
collapse of young blossom spurs and associated leaves. A gummy exudate is present at base of flowers. Gray brown spore masses develop on diseased flowers under high humidity.
Cankers form on the wood at the base of blossom spurs.

The fungus survives in mummies,
twig cankers, and remaining diseased flower parts and spurs. Spore pads
(sporodochia) on old infections also may provide inoculum for spring infection.
Spores are airborne or rain splashed. Optimum conditions for infection and
disease development are rainy weather during bloom with temperatures in the
mid-70s (0F). All flower parts are susceptible to infection, and
these infections may lead to blossom blight.

Unlike brown rot on peach and
nectarine, control of spring brown rot of prune does not appear to have any
effect on harvest levels of brown rot. However, in orchards with chronic
blossom and twig blight, spring applications are recommended.

Cultural Control
Good orchard sanitation helps
reduce the amount of brown rot inoculum in spring. Have pruning crews remove
all fruit mummies and blighted shoots. Remove the mummies from the orchard and
destroy them. If left on the orchard floor, mummies will produce inoculum in
the spring. You can cultivate the orchard floor to bury fruit mummies and
reduce inoculum production. Dense ground cover maintained during bloom favors
the production of inoculum by fruit mummies.

Chemical Control
Treat at green bud and again at full bloom. An intermediate treatment at the popcorn stage may be necessary if bloom is prolonged and
weather favors disease development. Fungicides are most effective when applied
before a rainfall and allowed to dry.

Common name

Amount to Use

R.E.I.+

P.H.I.+

(trade name)

(hours)

(days)

The following
materials are listed in order of usefulness in an IPM program, taking into
account efficacy. When choosing a pesticide, also consider information
relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.

A.

PROPICONAZOLE

(Orbit) 3.6EC

4 fl oz/acre

24

0

(Bumper) 41.8EC

4 fl oz/acre

24

0

MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)

COMMENTS: Most effective
when applied before a rainfall and allowed to dry. Apply at 5–10% bloom and make a second application at 80–100% bloom.

B.

PYRACLOSTROBIN/BOSCALID

(Pristine)

10.5–14.5 oz/acre

12

0

MODE OF ACTION GROUP NAME
(NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7)

C.

CYPRODINIL

(Vangard) 75WG

5 oz

12

2

MODE OF ACTION GROUP NAME
(NUMBER1): Anilinopyrimidine (9)

COMMENTS: Do not apply more than 10 oz/acre/year for blossom blight control.

D.

PYRIMETHANIL

(Scala) SC

18 fl oz

12

2

MODE OF ACTION GROUP NAME
(NUMBER1): Anilinopyrimidine (9)

COMMENTS: Do not apply more than 10 oz/acre/year for blossom blight control.

E.

IPRODIONE

(Rovral) 4F

1–2 pt/acre

24

0

MODE OF ACTION GROUP NAME
(NUMBER1): Dicarboximide (2)

COMMENTS: Addition of a
narrow range oil (superior, supreme) at 1–2% increases the effectiveness of this material and will aid in aphid control.

F.

THIOPHANATE METHYL

(Topsin-M) 70WP

8 oz/100 gal water

12

1

MODE
OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)

COMMENTS: Addition of a
narrow range oil (superior, supreme) at 1–2% increases the effectiveness
of this material and will aid in aphid control. Strains of Monilinia
fructicola resistant to
thiophanate methyl have been found in California. If resistance has occurred
in your orchard, do not use this fungicide. Use only 1 application of
thiophanate methyl/year, and always apply with a fungicide of different chemistry.

G.

FENHEXAMID

(Elevate)

1–1.5 lb/acre

12

0

MODE OF ACTION GROUP NAME
(NUMBER1): Hydroxyanilide (17)

COMMENTS: Apply when
conditions favor disease development. Do not apply more than 6 lb/acre/season.

H.

MYCLOBUTANIL

(Rally) 40W

2.5–6 oz

24

0

MODE
OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)

COMMENTS: Do not apply more than 2.75 lb/acre/season.

I.

CAPTAN 50WP

(Various)

4–6 lb

4 days

0

MODE OF ACTION GROUP NAME
(NUMBER1): Multi-site contact (M4)

COMMENTS: Do not apply in combination with, immediately before, or closely following oil sprays.

J.

CHLOROTHALONIL

(Echo 720, Bravo Weather Stik)

3.125–4.125 pt/acre

12

0

MODE OF ACTION GROUP NAME
(NUMBER1): Multi-site contact (M5)

COMMENTS: Do not apply in
combination with, immediately before, or closely following oil sprays. Do not use after jacket split.

K.

AZOXYSTROBIN

(Abound 2F)

12.3–15.4 fl oz

4

0

MODE OF ACTION GROUP NAME
(NUMBER1): Quinone outside inhibitor (11)

COMMENTS: Do not apply more
than 2 applications before alternating with a fungicide that has a different mode of action.

+

Restricted
entry interval (R.E.I.) is the number of hours (unless otherwise noted) from
treatment until the treated area can be safely entered without protective
clothing. Preharvest interval (P.H.I.) is the number of days from treatment
to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.

1

Group
numbers are assigned by the Fungicide Resistance Action Committee (FRAC)
according to different modes of actions (for more information, see
http://www.frac.info/). Fungicides with a different group number are suitable
to alternate in a resistance management program. In California, make no more
than one application of fungicides with mode of action Group numbers
1,4,9,11, or 17 before rotating to a fungicide with a different mode of
action Group number; for fungicides with other Group numbers, make no more
than two consecutive applications before rotating to fungicide with a different mode of action Group number.

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